Many portable, devices, for example mobile telephones, contain a number of acoustic transducers, such as microphones, earpieces and speakers. Such transducers are key components in mobile phone audio/acoustic design. Generally, there will be one or more sound channels or back cavities associated with each acoustic transducer. Such sound channels can ensure a certain frequency response is obtained for the transducer, and must be carefully designed as part of the mechanical configuration of the device hardware. Small changes in the size and configuration of the sound channels or cavities can have a large effect on the acoustic properties of the combined transducer/sound channel.
In known acoustic transducer configurations, the mechanical design of the sound channels is fixed at the point of hardware design and manufacture of the device is completed, and cannot be later adapted during use for a specific purpose or desired configuration. Instead, the desired acoustic properties are achieved by filtering the electrical signal representing the sound output before the signal is applied to the transducer. Typically, this requires the use of significant processing power, commonly provided by dedicated digital signal processors (DSPs).
Commonly, certain limitation and optimization modifications of the acoustic response of the transducer can be carried out in the DSP, in order to adapt the acoustic properties, as required during use of the device. However, this approach has problems, and it is difficult to overcome the restrictions imposed by the mechanical design of the transducer.
An example restriction imposed by the mechanical design is that certain configurations of directional microphone require two sound outlets designed in hardware around the microphone module. In some conditions, directional microphones are known to have better performance compared to omni-directional microphones. However, the reverse may be true under different conditions, for example directional microphones are known to be sensitive to windy conditions. As the hardware design of the microphone is fixed, any adaptation to the current conditions must be provided electronically.
Similarly, known earpiece designs may be conventional or leak tolerant. A true and efficient leak tolerant earpiece design provides an almost constant experience for playback of the downlink audio in different environmental conditions where a user seals the device containing the earpiece against their ear, where the seal achieved may not be perfect. Due to the leak tolerant nature of the earpiece, the leak between the handset and user's ear is almost not noticeable.
However, the mechanical design of an earpiece for a leak tolerant design is challenging, and a conventional design cannot be directly converted to leak tolerant design unless the mechanical design of the earpiece is reconsidered.
However, in some situations a leak tolerant earpiece design might not be preferred; for example, some users prefer a boosted low frequency response which is possible when a conventional earpiece design is provided in the handset. In addition, conventional earpiece designs provide a passive amplification which can sound louder if the user seals the handset against their ear very well.
According to current designs, the hardware integration requirements of the earpiece are different for leak-tolerant and conventional designs, and it is difficult, if not impossible, to configure a conventional earpiece to act as a leak tolerant earpiece once the hardware design has been fixed.
Other examples include handsfree speakers and other accessories where headsets are designed as open or closed back.
Thus, it would be beneficial to be able to adapt the mechanical hardware design of the transducer to adapt the acoustic properties during use of the device according to a desired operating mode for a device containing the transducer.
However, changing the properties of acoustic transducer, and especially miniature ones, is not a simple task. Previous attempts to provide flexibility in the configuration of transducers have generally required multiple transducers to be integrated into the system, and the inputs/outputs of the multiple transducers may then be combined through processing in a DSP to produce the required effect.
As discussed above, the frequency response of the transducer is dependent on the size and shape of the sound channels and cavities associated with the transducer. Thus, in known devices, the frequency response of transducers is fixed along with the integration of the hardware into a device. However, there exist situations in which it could be advantageous to be able to modify the frequency response.
For example, most of the energy of wind noise is known to be at low frequencies. Therefore, an omni-directional microphone's performance may also be poor in windy conditions, if it is designed to pick up low frequency sounds.
The requirements for acoustical properties of a speaker, or an earpiece, may vary depending on the situation. This can cause problems especially in applications where there is not enough resources (power, computing power) available to fix the output electrically.
However, if it were possible to modify the hardware configuration of the transducer, improved performance could be realised without processor intensive filtering.
In addition, it is common in current telephone applications to use narrow band codecs in which only a relatively small range of frequencies are recorded and transmitted over the phone network. However, some operators provide for the use of wideband codecs, in which a much larger range of frequencies are used. In order to support the use of wideband codecs, the handset should include hardware integration of transducers that support wideband operation. However, transducers optimized for wideband codecs may no longer be ideal for use with narrowband codecs, and vice versa. It would therefore be advantageous if it were possible to modify the hardware integration of the transducer during use to be optimized for operation with either wideband or narrow band codecs as required.